1. Field of the Invention
The invention relates to a reinforced molding material which contains a filler or a fibrous reinforcing material and a silane-grafted polyolefin.
2. Discussion of the Background
The reinforcement of thermoplastics by means of a filler or of a fibrous reinforcing material such as, for example, glass fibers, has long been part of the prior art. By means of this measure, the modulus of elasticity can be very effectively increased but the fracture behavior is often unsatisfactory, which is manifest, for example, in substantially reduced impact strength. In these cases, it was found that there is only poor binding or no binding at all between polymer matrix and reinforcing material. The tensile strength, too, is greatly dependent on the binding so that the full potential of this material combination can be utilized only in the case of strong interphase adhesion. This problem is encountered in particular in the case of molding materials based on polyolefins or polyesters.
One possibility for increasing the interphase adhesion between polymer matrix and reinforcing material is the use of a size. Although extensive work in this context has long been known, the result is still unsatisfactory in many cases, especially since the sizing of the reinforcing material constitutes an additional complication in the process.
Japanese patent application JP-A-58217532 states that glass fiber-reinforced polyolefin molding materials having excellent mechanical properties are obtained if a polyolefin is used which was subjected to free radical grafting with an aliphatically unsaturated trialkoxysilane.
Over and above the fact that this implies limitation to polyolefin molding materials, this method also has some disadvantages which prevent its use. On the one hand, the total matrix material is in fact remelted and is functionalized during this procedure, which gives rise to considerable additional process costs. In particular, a substantial amount of the expensive silane must be used, the unconverted proportion having to be removed subsequently. In addition, undesired changes in the melt viscosity result, free radical degradation taking place in the case of polypropylene and free radical synthesis in the case of polyethylene. In addition, the fact that the incorporation of glass fibers into a highly viscous polymer melt requires high shear forces is a general disadvantage, which may lead to a decrease in the molecular weight in the case of a matrix- in particular, however, this leads to considerable mechanical comminution of the fibers and hence to a deterioration in the mechanical properties. In general, establishing a desired specification in a controlled manner is virtually impossible in this way.
Japanese patent application JP-A-54064545 describes molding materials which contain
a) 100 parts by weight of polyolefin, PA1 b) from 2 to 100 parts by weight of a polymer in which a silane, for example, vinyltrimethoxysilane, has been grafted onto polyethylene, a copolymer based on ethylene or a halogenated polymer derived therefrom, and PA1 c) from 10 to 25 parts by weight of a reinforcing material. PA1 (a) from 0 to 98 parts by weight of one or more thermoplastics, PA1 (b) from 2 to 100 parts by weight of a substantially amorphous polyolefin which has been subjected to free radical grafting with a silane which has at least one olefinic double bond and one to three alkoxy groups bonded directly to the silicon, this grafted polyolefin having a melt viscosity at 190.degree. C. in the range from 100 to 50,000 mPas, measured on the basis of DIN 53 019 in a rotational viscometer at a shear rate of 30.5 s.sup.-1, the parts by weight of (a) and (b) summing to 100, and PA1 (c) from 0.5 to 400 parts by weight of a reinforcing material, with the exception of those molding materials in which less than 28 parts by weight of barite are used as reinforcing material. PA1 from 0 to 95% by weight of an .alpha.-olefin having 4 to 10 carbon atoms; PA1 from 5 to 100% by weight of propene and PA1 from 0 to 50% by weight of ethene. PA1 The substantially amorphous polyolefin particularly preferably has the composition: PA1 from 3 to 95% by weight of an .alpha.-olefin having 4 to 10 carbon atoms, PA1 from 5 to 97% by weight of propene and PA1 from 0 to 20% by weight of ethene. PA1 The .alpha.-olefin having 4 to 10 carbon atoms is in particular 1-butene, 1-hexene or 1-octene.
Here too, the incorporation of the reinforcing material into the highly viscous polymer melt is problematic.
A further, very specific molding material which consists of many components and contains a silane-modified polypropylene is described in German Offenlegungsschrift 41 36 687.